Strength of the moving ,arm of the loader is directly relative to the use properties and service life of the whole machine. The box-like structure is usually employed in the moving arm of mid-type wood loader, with the development of production, it has been changed to single plank moving arm. The modern design is adopted in exact strength analysis and research of structure design. This paper provides us with reliable basis and scientific design method of single plank moving arm changed for mid-type wood loader.